Flexural performance of a precast concrete slab with steel fiber concrete topping

The positive effects of various types of fibers on concrete ductility and other engineering properties, such as the tensile, flexural, fatigue, and load-bearing capacity after cracking and toughness, are well known. Steel fiber-reinforced concrete (SFRC) has been used increasingly in recent years and has been applied to various structural components. Considerable interest has been developed in using steel fibers in concrete to increase the load-carrying capacity of the structural members in service. It has been used recently to increase the flexural capacity of concrete slabs by applying a thin layer of SFRC onto an existing slab, a technique known as cement-base bonded overlay. The objective of this research is the investigation of the flexural behavior of a precast concrete slab with a steel fiber concrete topping. To reinforce the concrete overlay, hooked-end steel fibers with a length of 30 mm and a diameter of 0.75 mm were used. Because the performance of this composite slab depends on the bonding between the old and new concrete, different types of roughness at the interface has used to provide good bonding between the two layers. Based on experimental tests, the flexural performance was shown to depend not only on adding the steel fibers to the topping but also on the type of interface roughness. To examine the composite behavior of the specimens, the interface slip was also measured throughout the test. The results showed a good reliability of roughness in providing bonding strength at the interface. It was also found that roughness in the transverse direction provides the best bonding strength at the interface. Although the results showed interface slip at mid-span, slip was not detected at either end of the specimen.